Climatic Implications of Loess Deposits from the Beijing Region

Home , Environment of China, Loess Plateau

JOURNAL OF QUATERNARY SCIENCE (2001) 16(6) 575–582 Copyright  2001 John Wiley & Sons, Ltd. DOI: 10.1002/jqs.618

Climatic implications of loess deposits from the Beijing region

SHANGFA XIONG∗, ZHONGLI DING and TUNGSHENG LIU Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

Xiong, S., Ding, Z. and Liu, T. 2001. Climatic implications of loess deposits from the Beijing region. J. Quaternary Sci., Vol. 16 pp. 575–582. ISSN 0267-8179. Received 10 August 2000; Revised 10 January 2001; Accepted 19 January 2001

ABSTRACT: Variations in magnetostratigraphy, pedostratigraphy, grain size and magnetic susceptibility of the loess deposits near Beijing have been studied at two sections. The sections are about 400 km east of the main loess deposits in China, have a maximum thickness of 100 m and extend back to 1.1 Ma. The sequence consists of 14 loess–palaeosol couplets (S0-S14), which correlate well with sequences in the Loess Plateau. Susceptibility records from the sites near Beijing are comparable to the Xifeng, Luochuan and Baoji sections located in the middle part of the Loess Plateau; however, the down-core variations in the grain size in the Upper Lishi Formation exhibit some differences. Journal of Quaternary Science The median grain size increases by about 25–30 µm from L4 to L2, with the sandy grains (>63 µm) increasing from 10–20 wt% to 40–50 wt% . This implies that the depositional environment of the dust sources in the Beijing loess section is different in some aspects from the Loess Plateau. The Beijing loess may have had a different dust source than the Loess Plateau. Copyright  2001 John Wiley & Sons, Ltd.

KEYWORDS: loess; Beijing; susceptibility; grain size; desert.

Introduction Previous studies have shown that loess deposits are widely distributed in China, within and beyond the Loess Plateau (Liu et al., 1965, 1985). The study of loess deposits outside Chinese loess is an important archive of climatic and the Loess Plateau should enhance our understanding of environmental changes over East Asia during the Quaternary loess depositional processes and palaeoclimatology outside (Liu et al., 1985; Kukla et al., 1988; Liu and Ding, 1998; the Loess Plateau, and the connection between the loess Kukla and An, 1989; Rutter et al., 1990; An et al., 1991; depositional regions and the deserts. However, little attention Ding et al., 1992, 1994; Xiao et al., 1995). The main has been paid to the loess deposits beyond the Loess Plateau. body of information about Chinese loess stratigraphy and Here we investigate the loess deposits in the Beijing region. palaeoclimatology is from the Loess Plateau in the central part The Beijing region is an important site of loess deposition of northern China (Liu et al., 1985; Kukla and An, 1989; Rutter east of the Loess Plateau (von Richthofen, 1882; Andersson, et al., 1990; Ding et al., 1992). Studies during the last two 1939; Barbour, 1929; An and Lu, 1984; Liu et al., 1985; Lu decades have revealed that climatic cycles, represented by the et al., 1987). Based on magnetostratigraphic, pedostratigraphic loess–palaeosol alternations, are dominated by variations in and sedimentological approaches, a correlation between the monsoon circulation over East Asia, which show a coherent loess near Beijing and that in the Loess Plateau is made here. variability with respect to global ice-volume cycles (An et al., In addition, palaeoclimatic implications and the connections 1991; Ding et al., 1992, 1994, 1995). The loess deposits in with the desert source areas are also discussed. the Loess Plateau commonly are believed to be derived from deserts west and/or north of the plateau (Liu et al., 1965, 1982, 1985; Zhang et al., 1994; Ding et al., 1999). Thus the Loess Plateau and the deserts can be regarded as a coupled Geological setting environmental system in terms of a sediment source and sink relationship. The study area is located in the northwest part of Beijing, in the eastern part of North China (40°30 N, 115°10 E; Fig. 1). The * Correspondence to: Shangfa Xiong, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China. E-mail: xiongsf@public2. mean annual precipitation is approximately 500–680 mm, east.net.cn and primarily occurs during summer. The mean annual temperature is approximately 8–12.1°C, with the highest Contract/grant sponsor: National Key Project for Basic Research (China); Contract/grant number: G1998040800. temperature occurring during July and the lowest temperature Contract/grant sponsor: National Science Foundation of China; Contract/grant in January. Geomorphologically, the Bejing region is marked number: 49894170. by an alternation of mountains and sedimentary basins. 576 JOURNAL OF QUATERNARY SCIENCE

100° 105° 110° 115° 120° 115°E 116°E A B 0 10 20 30km 45° 45° C Mongolia Zhangjiakou Hunshandake desert

° ′ Yellow River 40°40′N 40 40 N 40° Beijing 40°

Loess Plateau Sanggan River YanqinHuailai-Zhoulu Basin Fanshan Yongding River ° Lanzhou Yellow River 35 Luochuan 35° 0 200 400km Baoji ° ° ° ° 120° 115°E 116°E 100 105 Xi’an 110 115 Zhaitang D

Lacustrine Fluvial Modern Bedrock or Gobi Desert Loess sediment sediment Lake other sediments

Figure 1 Location map for Beijing (A) with an inset map (B) showing loess distribution near the Beijing region (cross-section C–D is shown in Fig. 2)

Figure 2 A transect from northwest to southeast across the loess deposits in the Beijing region

The largest basin is the Yanqin-Huailai-Zhoulu Basin (YHZ Beijing region (Fig. 2). These loess-mantled terraces can be basin). The most proximal desert is the Hunshandake desert used for reconstructing the history of the river aggradation and (21 400 km2), which lies to the northwest. downcutting (Porter et al., 1992). The terraces are designated

The present margin of the Hunshandake desert is about T1 to T6, with the oldest one being T6. The T6 terrace is found 180–200 km northwest of the loess deposits in the Beijing on the margin of the YHZ basin. The top of this terrace is region. Most of the sand dunes in the Hunshandake desert covered by loess units L15 to L1. Terrace T5 also is found on are inactive or have been anthropogenically reactived at the margin of the YHZ basin as well as adjacent to some river present. Holocene sandy soils are present near the centre of banks. It is covered by loess units S9 to S0. Terraces T4,T3,T2 the desert. However, during glacial periods the Hunshandake and T1 are widely distributed, and are overlain by S5, S2, S1 desert probably was covered by shifting dunes and was a and L1, respectively. source of dust for the loess deposits (Sun et al., 1998). Six Typical loess features are observed in deposits 180–280 km terraces have been recognised in the loess-covered area of the southeast of the Hunshandake desert, whereas transitional

Copyright  2001 John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 16(6) 575–582 (2001) LOESS IN THE BEIJING REGION 577 aeolian sandy–loess deposits were observed about 90 km Magnetostratigraphy and pedostratigraphy south of the desert. The loess occurs mainly on uplands along the piedmonts of the mountains and covers terraces of different heights. The loess is commonly about 10–20 m The magnetic reversal stratigraphy of the Fanshan section is thick, with a maximum thickness of about 100 m. The loess illustrated and correlated with the well-established geomag- deposits thin from the YHZ basin in the north towards the netic polarity time-scale (Cande and Kent, 1995) in Fig. 3. The south. Loess sections were described and sampled at numerous section covers the Brunhes normal and part of the Matuyama localities on the oldest terrace (T6) in the Beijing region. reversed polarity zone. The magnetic reversal sequence is The thickest loess deposit, the Fanshan section, is located similar to that determined previously at Luochuan (Heller and in the southern part of the YHZ basin. This section consists Liu, 1982; Liu et al., 1985; Kukla and An, 1989), Xifeng (Liu of 14 loess–palaeosol couplets and is underlain by fluvial et al., 1987; Kukla and An, 1989), Xi’an (Zheng et al., 1992) pebbly conglomerates. Other loess sections, including the and Baoji (Rutter et al., 1990; Ding et al., 1993). The Brun- Zhaitang section, located 70 km northwest of Beijing (the hes–Matuyama magnetic reversal is observed in soil unit S8 type section of the Malan Loess formation), also have been (66.5 m). The upper and lower reversals of the Jaramillo sub- investigated. chron are assigned respectively within soil unit S9 (74 m) and S12 (88 m). A few data points apparently yield normal polarity above the Jaramillo (Fig. 3). This feature also can be seen in the magnetostratigraphy of the Baoji section (Rutter et al., 1991); Methods the normal polarity data points may be overprinted samples that have not responded to laboratory cleaning (Heller and Evans, 1995). By linear extrapolation, the age of the base of The recognition of distinct palaeosol units has been used to the Fanshan section is about 1.18 Ma. differentiate the loess–palaeosol units in the Beijing sections Most of the sections are composed of the Malan Loess (Rutter et al., 1991; Ding et al., 1992). The Si–Li system was Formation and the Upper Lishi Loess Formation, whereas the used to label the alternations of palaeosols and loess (Liu et al., Fanshan section consists of the Malan Loess, the Upper Lishi 1985; Rutter et al., 1991). Loess and the Lower Lishi Loess. Palaeomagnetic measurements were made at the Paleo- The upper unit at Fanshan section is S0, termed the magnetism Laboratory, Institute of Geology and Geophysics, Black Loam, and has a maximum thickness of about 2–3 m. Chinese Academy of Sciences, with a 2-G three-axis cryogenic Owing to extensive agricultural activity, however, the unit magnetometer; a total of 110 samples was measured. Some of generally is absent or only preserved as a residual layer the samples were thermally demagnetised at 50 °C steps up to at most localities. Typically, S0 exhibits a fine to medium 600 °C. Almost all of the samples obtained a stable magnetic granular to fine subangular structure, common to many component above 300–400 °C, and we used this demagneti- rhizomyceliums, and contains rare to common root tubules sation level to determine the natural remanent magnetisation (commonly <1 mm in diameter). Below S0 is the Malan Loess (NRM) directions for all the samples. Magnetic susceptibility (L1). In the Beijing region, the Malan Loess is composed of was measured with a Bartington MS2 susceptibility meter. silt and silty clay, with very weak pedogenic modification Particle size distribution was determined with a Sald- (Table 1). It exhibits a subangular blocky to very coarsely 3001 diffraction particle analyser after the samples had been prismatic structure, rare to common rhizomycelium, and rare ultrasonically treated in a 20% (NaPO3)6 solution. root tubules. No primary sedimentary structures have been

Stratigraphy NRM(10−6 Am2 kg−1) DEC (°) INC (°) Observed Cande & Kent 02040−90 090 180 270−90 −45 09045 Polarity (1995) 0 S0

10 S1 20

40 C1n S5 50

Depth (m) 60 B S8 0.78Ma 70 M 0.99Ma 80 ) J C1r.1n 90 S12 1.07Ma

100 S14 110

Figure 3 Pedostratigraphic column, magnetic polarity, natural remanent magnetisation (NRM), declination (DEC) and inclination (INC) of the Fanshan loess section

Table 1 Correlation of the pedogenic characteristics between the Beijing loess with the loess in the Loess Plateau (data are from Baoji (Rutter et al., 1991; Ding et al., 1993), Luochuan (Kukla and An, 1989) and Lanzhou (Chen and Zhang, 1993): A, clay skins ( ) and ferromanganese coatings ( ); B, carbonate nodules ( ), carbonate impregnation ( ), gypsum crystals ( ); C, palaeosol color hue ( 7.5YR; 5YR)

Beijing section Baoji section Luochuan section Lanzhou section A B C A B C A B C A B C

Black Loam S0 Malan Formation L1 Upper Lishi Formation S1 ?

L5 Lower Lishi Formation S5-1 S5-2 S5-3

L6 S6 L7 S7 L8 S8

L9 S9 L10 S10 L11 S11 L12 S12 L13 S13 L14 S14 L15

recognized in the Malan Loess. In the study area the Malan to many, clay skins. A layer of CaCO3 nodules 30–50 cm thick Loess is up to 12–15 m thick. The median grain size (Md) is developed below S3 and S4. ranges from 35 to 50 µm, with a sandy loam to loamy loess The Lower Lishi Formation (Table 1) comprises 10 loess–pa- texture. laeosol couplets (S5–L15) in the study region. The loess in The Upper Lishi Formation (Table 1) consists of four this formation is strong brown to yellowish brown (7.5YR loess–palaeosol couplets (S1–L5) in the Beijing region. The 5/6 to 10YR 5/6), with blocky to prismatic structure, rare loess within this formation is light yellowish brown to brownish rhizomycelium and rare root tubules. The palaeosols exhibit a yellow (10YR 6/4 to 10YR 6/6), and exhibits a coarse blocky to yellowish red to dark brown colour (5YR 4/6 to 7.5YR 3/4), with coarse prismatic structure, common to many rhizomycelium prismatic to blocky structure, rare to common rhizomycelium and rare to common root tubules. No primary sedimentary and rare to common clay skins. Below most of the palaeosols, structures have been observed in the Upper Lishi Formation. there is a layer of pedogenic CaCO3 nodules with diameters There are four buried palaeosols in the Upper Lishi Formation, of about 5–20 cm. designated S1, S2, S3 and S4. The palaeosols typically are As in the Loess Plateau, the Malan Loess and Lishi Loess brown to strong brown (7.5YR 5/4 to 5YR 4/6), and exhibit ﬁne Formations are characterised by numerous buried argillic prismatic to ﬁne subangular blocky structure, rare to common palaeosols with leaching of CaCO3. The soil ‘A’ horizons rhizomycelium and rare to common root tubules. Units S1 to are not well preserved in most cases, and below the Bt or

S4 are considered buried argillic horizons (Bt) with common, Bw horizons, there commonly is a layer of CaCO3 nodules,

µ indicating leaching and transportation of CaCO3 within the Malan Loess. The variation in the >63 mgrainsmaybe sequence. The most developed palaeosol, S5, however, has an indicator of proximity to the source (Ding et al., 1999) in no layer of CaCO3 nodules below the base, perhaps implying addition to variations in transporting wind speed and/or lack of extreme pedogenesis. Some of the palaeosols are polygenetic. pedogenesis. The magnetic susceptibility indicates enhanced For example, S5 consists of three palaeosols, whereas S1, S2, pedogenesis during interglacial and interstadial periods (Liu S6 and S9 consist of two palaeosols. These features are similar et al., 1988; Zhou et al., 1990) (Fig. 4). At the same time, the to those observed in the Loess Plateau, and imply widespread proximal dust source areas also may have been inﬂuenced and stable environments during these periods of time. by the summer monsoon circulation and no longer provide a major part of dust particles to the downwind regions.

Variations in the climatic proxies during past 1.1 Ma Last1.1 MA

The sequential variation of proxies in the Fanshan section Last interglacial–glacial cycle is shown and correlated with the oxygen isotope record of ODP site 846 (Mix et al., 1995) and orbitally tuned The Zhaitang section comprises the Malan Loess (Fig. 4) and ages for Baoji loess (Ding et al., 1994) (Fig. 5). In general, soil unit S1 (the upper part of S1 was dated as 84 ± 9kaby the variation in magnetic susceptibility tracks the loess and a thermoluminescence technique, Lu et al., 1987). The grain palaeosol alternations, with palaeosols corresponding to the size proﬁle displays frequent oscillations superimposed on peaks and the loess to the troughs. No long-term trends, or the trend of orbital-scale cyclicity, as evidenced in other shifts in the overall mean, are displayed in the susceptibility loess sections (Liu and Ding, 1998) (Fig. 4). The median record. Over the past 1.1 Ma grain sizes are larger in loess grain size of palaeosol S1 (equivalent to marine oxygen units than in palaeosols. A notable trend is that the median isotope stage (OIS) 5) and a poorly developed soil within grain size (Md) and the percentage of coarse grains (>63 µm) loess L1 (marine OIS 3) is ﬁner than 15 µm, whereas the increases abruptly from the lower part to the upper part of L3, sediments in L1 are coarser than 35 µm. The percentage corresponding to about 265 ka by correlation with the oxygen of grains larger than 63 µm generally tracks the Md curve isotope record of ODP site 846 (Mix et al., 1995) and the and demonstrates similar glacial–interglacial variability, with age model of the Baoji loess (Ding et al., 1994). The median 0–10% >63 µm by weight in soils, and 15–30% in the diameter of loess from L15 through L4 is about 20–30 µm,

OIS 2 OIS 3 OIS 4 OIS 5 S0 L1 S1 )

120 1 − kg 100 3 m 8 − 80

60 12

40 Susceptibility (10 ) 10 % m ( µ 8 2 <

6 0 Grains Grains )

4 % 10 m ( µ 63

20 >

10 Grains Grains m) 30 µ

40 Median grain size ( size Median grain 02468101214 Depth (m)

Figure 4 Variations in magnetic susceptibility and grain size during the last interglacial–glacial cycle in the Zhaitang section

3 Site 846 δ 18O to PDB (‰) 4

5 2 Baoji loess

1 Grain size (<2 µm/ 0 >10 µm) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

Age (Ka BP) 200

)

− kg

100 3

m 8

80 −

Susceptibility

(10 µ

) S5 L12S12 L13 S13 S14 L15

5 5 S0 L1S1 L2 S2 S3 S4 L5 L6S6 L9 S9 S10 % < 40 0

(wt (wt 80

m µ

Grains Grains 0

) )

10 10 %

80 40 <

(wt (wt

m Grains Grains

µ 0

) )

63 63 %

> 40 (wt (wt

100 Grains Grains

) )

35 35 % 50 >

(wt (wt Grains Grains

m) m) 40

( Median grain size grain Median 0 0 20 40 60 80 100 120 Depth (m)

Figure 5 Correlation of the susceptibility and grain size of the Fanshan loess with oxygen isotope data for ODP site 846 (Mix et al., 1995),  Ocean Drilling Program. Reproduced with permission; and the orbitally tuned ages for the Baoji loess section (Ding et al., 1994).  Elsevier Science. Reproduced with permission. An abrupt shift in grain size is observed at 265 ka and is marked with a dashed line

25 30 A B 25 20 20

) 15 ) % % 15 10 10

Frequency ( Frequency 5 ( Frequency 5

0 0 0.25 0.98 3.9 15.6 62.5 250 0.25 0.98 3.9 15.6 62.5 250 Grain size (mm) Grain size (mm)

Figure 6 Typical grain-size distributions of the loess before (A) and after (B) the abrupt shift in the grain size throughout the Fanshan loess section whereas from L3 to L1 it is 45–60 µm. The percentage of the Before and after the abrupt shift the grain-size distributions grains >63 µm increased at the same time from 10–20 wt% have changed. Below L3, typical distributions of grain size to 40–50 wt%. are ﬁnely skewed with a modal size of about 44 µm.

Above L3, the distributions is characterised by a modal size Discussion and conclusions of 62.5 µm (Fig. 6). For palaeosol horizons, the grain-size distributions are similar from the top to the base in the Fanshan section. Previous studies have shown that the pedostratigraphy of different loess sections in the middle part of the Loess Plateau are well correlated (Ding et al., 1992, 1994). Loess deposits are inferred to have accumulated during times Correlation with Luochuan, Lanzhou and of strengthened winter monsoon and weakened summer Baoji sections monsoon, whereas the palaeosols developed when these conditions were reversed (An et al., 1991; Ding et al., 1992, 1994). Spectral analyses have suggested that the first-order Pleistocene climate variations recorded in the loess–palaeosol Thickness of loess and pedogenic intensity in palaeosols in sequence exhibit orbital periodicities, and that the 100 kyr the Beijing region are similar to corresponding loess units and cycle was restricted to loess deposited during the past 1.2 Myr palaeosols at sites in the Loess Plateau. (Ding et al., 1994). This implies astronomical control and/or The thickness of the loess–palaeosol couplets in the ice-volume forcing of the monsoonal climatic changes over Beijing region seems similar to that in the middle part of the Loess Plateau. the Loess Plateau, but is thinner than that in the Lanzhou The similarity in pedostratigraphic and sedimentary proper- section (Chen and Zhang, 1993). For example, the Lishi ties between the Beijing loess and the Loess Plateau implies Loess Formation in Beijing (S5–S14; L15 is not preserved) that they are similar in mode of deposition and source and is about 60 m thick, slightly thicker than that in the Baoji in pedogenic environment. We infer that the same climatic (S5–S14, 46.9 m; Rutter et al., 1991; Ding et al., 1992, 1993) processes found in the middle part of the Loess Plateau also and Luochuan sections (S5–S14, 38.6 m; Liu et al., 1985; may have controlled the dust deposition and the soil formation Kukla and An, 1989), whereas in the Lanzhou section it in the Beijing region. As in the Loess Plateau, deposition in increases to 134.7 m (S5–S14). The thickness of the Malan the Beijing region occurred during glacial periods when the Loess Formation in the Beijing region is about 12 m, slightly winter monsoon was strengthened, whereas the palaeosols thicker than that in the Baoji section (6.8 m) and Luochuan were developed during interglacial periods when the summer section (8 m), but much thinner than that in the Lanzhou monsoon dominated. The number of loess–soil cycles in the section (51.5 m). It seems that the average loess deposition Loess Plateau is identical to those in the Beijing region. There rate in the Beijing region is similar to that in middle part of the are nine major soils recognized above the Brunhes–Matuyama Loess Plateau. reversal in both regions, with three subunits for the S5 soil com- A comparison of the pedogenic properties of the palaeosols plex and two subunits for the S2 soil complex. The sequential between the Beijing section and other sections in the Loess pattern of pedogenic strength is also the same for deposits Plateau was undertaken and is shown in Table 1. The Beijing in both regions. However, the loess deposits in the Beijing section compares well with the Baoji and Luochuan sections region differ from those in the Loess Plateau with respect to in the following aspects: susceptibility and grain-size variations. In the Loess Plateau, the dust source areas are the deserts to the northwest of the 1 there is an apparent decreasing trend in pedogenic develop- plateau, with a concomitant decrease in grain size towards the ment from S5 to S1, based on the development of the clay southeast (Liu et al., 1965, 1985; Ding et al., 1999). On the skins and the variation in magnetic susceptibility; other hand, pedogenic development is controlled by the sum- 2 the pedocomplexes, S5 and S2, are composed of three and mer monsoon climate, which produces a decreasing gradient two subunits, respectively—for S2 the upper subunit is more from southeast to the northwest (Kemp, 1999). Thus, grain strongly developed than the lower subunit, for S5 the most size is coarsest in the sections where the pedogenic develop- developed subunit is S5-1 whereas S5-2 is the most poorly ment is weakest, whereas maximum palaeosol development is developed and S5-3 is moderately developed; associated with the finest grain size. For example, loess in the 3 the Bt horizons of the more developed palaeosols are rich Lanzhou section (Chen and Zhang, 1993) is much coarser than in clay skins and ferromanganese coatings, and at the bases in the Baoji section (Ding et al., 1994), whereas the palaeosols of most palaeosols carbonate nodules are present. in the former are much weaker than in the latter. The Beijing section, however, exhibits pedogenic development as strong In general, the pedogenic intensity for the palaeosols in the as Luochuan and Baoji, whereas the grain size at Beijing is as Beijing section is between that of Baoji and Luochuan, based coarse as the Lanzhou section, but with a lower accumulation on the development of the clay skins and the soil structures. rate. This implies that the mode of deposition and source in These three sections show much more pedogenic development the Beijing loess section is different from the Loess Plateau. than the Lanzhou section. In addition, variations and shift in grain size (median The variations in grain size and susceptibility throughout diameter and wt% of the grains >63 µm) at Beijing do the Beijing section are consistent with those of the Luochuan not coincide with the changes in magnetic susceptibility and Baoji sections, where systematic differences in proxy and pedogenic characteristics. This effectively rules out the data are attributable to glacial–interglacial cyclic variations possibility of variations in pedogenesis in controlling the in the intensities of the summer and winter monsoons. variations in grain size. Meanwhile, the abrupt shift in grain The most significant difference in climatic proxies between size is not observed in other loess sections in the middle the Beijing section and the sections in the central Loess part of the Loess Plateau. This indicates that a variation in Plateau is that there is an abrupt increase in the grain size regional atmospheric circulation (for example, variations in in the Upper Lishi Formation (L3) in the Beijing section, wind speed), which would influence a large area, is not the whereas this increase is not observed in the Luochuan main factor controlling the changes in grain size. Previous and Baoji sections. This may imply the influence of a studies suggested that grains >63 µm cannot be transported different regional factor for loess deposition in the Beijing long distances even in extreme dust storm conditions (Pye, region. 1987), and may be used as an indication of proximal dust

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